Highly stable [MaMbF6-n(O/H2O)n(Ligand)2(solvent)x]n Metal Organic Frameworks

ABSTRACT

Embodiments of the present disclosure describe metal-organic framework compositions comprising a pillar characterized by the formula (MbF5(O/H2O)), where Mb is selected from periodic groups IIIA, IIIB, IVB, VB, VIB, and VIII; and a square grid characterized by the formula (Ma(ligand)x), where Ma is selected from periodic groups IB, IIA, IIB, IIIA, IVA, IVB, VIB, VIIB, and VIII, ligand is a polyfunctional organic ligand, and x is 1 or more; wherein the pillaring of the square grid with the pillars forms the metal-organic framework.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/564,909 filed Oct. 6, 2017, which is a National Stage Application ofPCT Application No. PCT/IB2016/051992, filed on Apr. 7, 2016, whichclaims priority to U.S. Provisional Application No. 62/144,156, filed 7Apr. 2015, which application is incorporated herein by reference.

BACKGROUND

Today there is an increasing global desire to reduce greenhouse gasemissions and develop clean alternative vehicle fuels. Methane (CH4),the primary component of natural gas (NG), is of particular interest asit is abundant and has lower carbon dioxide (CO2) emission and moreefficient combustion than other hydrocarbons due its high H/C ratio.Biogases, including landfill gas, are also seen as promising renewableenergy resources, but, like NG, they contain significant amounts ofwater, CO2, and hydrogen sulfide (H2S) which must be removed beforebeing transported, stored, and burned as a fuel. For example, NG mustcontain less than 1-2% CO2 and 4 ppm H2S to meet fuel gas specificationsfor pipeline transportation. Within many industries, gas dehydration andremoval of CO2 and H2S remain some of the most intensive and challengingseparations, in part due to the intolerance of many technologies towater and H2S.

Available technologies for refining NG and other biogases are oftencostly, multi-stage processes. Amine scrubbing is a common liquid phasesystem used to remove acid gases such as CO2 and H2S from NG. However,stagnant historical operating efficiencies, and the excessive oxidativedegradation, evaporation, and the corrosive nature of the alkanolamineaqueous solutions create a myriad of performance, safety, andenvironmental concerns. Solid, porous material systems, such as zeoliteand metal organic frameworks (MOFs), offer more environmentally friendlyalternatives for CO2 capture, but require cumbersome, multi-stageprocesses. For example, zeolite has single-species selectivity for CO2and cyclic adsorption performance in the presence of moisture thatrequire prior dehydration and H2S removal stages. MOFs, similarly, canbe designed for CO2 capture, but most MOF structures reported so farexhibit prohibitively low stability for water and H2S.

MOFs generally include porous crystals which are assembled from modularmolecular building blocks, and provide a wide array of advantageousmaterial properties, including high surface area, porosity, stability,and sorption potential. While the available building block options, andcombinations thereof, are virtually limitless, such potential highlightsthe statistical difficulty in identifying and assembling MOFs withdesired and particularized material properties.

SUMMARY

In general, embodiments of the present disclosure describe metal-organicframeworks comprising pillars and square grids.

Embodiments of the present disclosure describe metal-organic frameworkcompositions comprising a pillar characterized by the formula(M_(b)F₅(O/H₂O)), where M_(b) is selected from periodic groups IIIA,IIIB, IVB, VB, VIB, and VIII; and a square grid characterized by theformula (M_(a)(ligand)_(x)), where M_(a) is selected from periodicgroups IB, IIA, IIB, IIIA, IVA, IVB, VIB, VIIB, and VIII, ligand is apolyfunctional organic ligand, and x is 1 or more; wherein the pillaringof the square grid with the pillars forms the metal-organic framework.

Embodiments of the present disclosure describe a metal-organic frameworkcomprising a pillar characterized by the formula (M_(b)F₅(O/H₂O)), whereM_(b) is selected from periodic groups IIIA, IIIB, IVB, VB, VIB, andVIII; and a square grid characterized by the formula(M_(a)(ligand)_(x)), where M_(a) is selected from Zn²⁺, Co²⁺, Ni²⁺,Mn²⁺, Zr²⁺, Fe²⁺, Ca²⁺, Ba²⁺, Pb²⁺, Pt²⁺, Pd²⁺, Ru²⁺, Rh²⁺, Mg²⁺, Al⁺³,Fe²⁺, Fe⁺³, Cr²⁺, Cr³⁺, Ru²⁺, Ru³⁺, and Co³⁺, the ligand is apolyfunctional organic ligand, and x is 1 or more; wherein the squaregrid and pillar associate to form the metal-organic framework.

Embodiments of the present disclosure describe a metal-organic frameworkcomprising a pillar characterized by the formula (M_(b)F₅(O/H₂O)), whereM_(b) is selected from periodic groups IIIA, IIIB, IVB, VB, VIB, andVIII; and a square grid characterized by the formula(M_(a)(ligand)_(x)), where M_(a) is selected from periodic groups IB,IIA, IIB, IIIA, IVA, IVB, VIB, VIIB, and VIII, where the ligand isselected from pyrimidine, pyridazine, triazine, thiazole, oxazole,pyrrole, imidazole, pyrazole, triazole, oxadiazole, thiadiazole,quinoline, benzoxazole, and benzimidazole, where x is 1 or more; whereinthe square grid and pillar associate to form the metal-organicframework.

Embodiments of the present disclosure describe a metal-organic frameworkcomprising a pillar characterized by the formula (M_(b)F₅(O/H₂O)), whereM_(b) is selected from Al⁺³, Ga³⁺, Fe⁺², Fe⁺³, Cr²⁺, Cr³⁺, Ti³⁺, V³⁺,V⁵⁺, Sc³⁺, In³⁺, and Y³⁺; and a square grid characterized by the formula(M_(a)(ligand)_(x)), where M_(a) is selected from periodic groups IB,IIA, IIB, IIIA, IVA, IVB, VIB, VIIB, and VIII, where the ligand is apolyfunctional organic ligand, and x is 1 or more; wherein the squaregrid and pillar associate to form the metal-organic framework.

The details of one or more examples are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description and drawings, and fromthe claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate non-limiting example embodiments ofthe invention.

FIG. 1A illustrates a schematic of an inorganic chain, according to oneor more embodiments of this disclosure.

FIG. 1B illustrates a schematic view of a metal organic framework,according to one or more embodiments of this disclosure.

FIG. 2 illustrates a method of fabricating a metal organic framework,according to one or more embodiments of the disclosure.

FIG. 3A illustrates powder X-ray diffraction data of a metal organicframework, according to one or more embodiments of this disclosure.

FIG. 3B illustrates powder X-ray diffraction data of a metal organicframework, according to one or more embodiments of this disclosure.

FIG. 4A illustrates a restricted pore aperture of an NbOFFIVE-1-Ni MOF,according to one or more embodiments of this disclosure.

FIG. 4B illustrates an expanded pore aperture of an NbOFFIVE-1-Ni MOF,according to one or more embodiments of this disclosure.

DETAILED DESCRIPTION

The present invention is described with reference to the attachedfigures, wherein like reference numerals are used throughout the figuresto designate similar or equivalent elements. The figures are not drawnto scale and they are provided merely to illustrate the invention.Several aspects of the invention are described below with reference toexample applications for illustration. It should be understood thatnumerous specific details, relationships, and methods are set forth toprovide an understanding of the invention. One skilled in the relevantart, however, will readily recognize that the invention can be practicedwithout one or more of the specific details or with other methods. Inother instances, well-known structures or operations are not shown indetail to avoid obscuring the invention. The present invention is notlimited by the illustrated ordering of acts or events, as some acts mayoccur in different orders and/or concurrently with other acts or events.Furthermore, not all illustrated acts or events are required toimplement a methodology in accordance with the present invention.

As used herein, “fluids” can refer to a gas, liquid, or combinationthereof. A gas or liquid can include one or more components. Forexample, a fluid can include a gas stream comprising CO₂, H₂S and watervapor.

As used herein, “refining” refers to removing one or more unwantedcomponents or separating one or more components from remainingcomponents of a composition, such as a fluid. For example, refining caninclude removing a fraction of H₂S from a fluid, such as natural gas.

As used herein, “poly-functional” refers to the characteristic of havingmore than one reactive or binding sites. For example, a poly-functionalligand can attach to a metal ion in multiple ways, bridge multiple metalions, or combinations thereof. Specifically, pyrazine is apoly-functional ligand.

As used herein, “water” or “H2O” can include solid, liquid, or vaporphases.

Gas storage and separation using porous materials has experiencedsignificant development in recent years in various industrialapplications related to energy, environment, and medicine. Among porousmaterials, metal organic frameworks (MOFs) are a versatile and promisingclass of crystalline solid state materials which allow porosity andfunctionality to be tailored towards various applications. MOF crystalchemistry uses a molecular building block (MBB) approach that offerspotential to construct MOFs where desired structural and geometricalinformation are incorporated into the building blocks prior to theassembly process.

Generally, MOFs comprise a network of nodes and ligands, wherein a nodehas a connectivity capability at three or more functional sites, and aligand has a connectivity capability at two functional sites each ofwhich connect to a node. Nodes are typically metal ions or metalcontaining clusters, and, in some instances, ligands with nodeconnectivity capability at three or more functional sites can also becharacterized as nodes. In some instances, ligands can include twofunctional sites capable of each connecting to a node, and one or moreadditional functional sites which do not connect to nodes within aparticular framework. A MBB can comprise a metal-based node and anorganic ligand which extrapolate to form a coordination network. Suchcoordination networks have advantageous crystalline and porouscharacteristics affecting structural integrity and interaction withforeign species (e.g., gases). The particular combination of nodes andligands within a framework will dictate the framework topology andfunctionality. While essentially limitless combinations of nodes andligands exist, to date, very few MOF materials are H₂S stable whichconsequently preclude their use in separation of gases containing eventraces of H₂S.

As disclosed in co-owned U.S. Application No. 62/044,928, a series ofisoreticular MOFs with periodically arrayed hexafluorosilicate (SiF6)pillars, called SIFSIX-2-Cu-i and SIFSIX-3-Zn, SIFSIX-3-Cu andSIFSIX-3-Ni showed particularly high CO₂ selectivity and capture. Theseproperties in SIFSIX-3-M materials suggest broad applications from ppmlevel CO₂ removal to bulk CO₂ separation. However, with the exception ofSIFSIX-3-Ni, the SIFSIX-3-M materials were not tolerant to H₂S. Andalthough these materials exhibit high structural stability in thepresence of CO₂, extensive exposure of all SIFSIX-3-M materials tomoisture detrimentally induces a phase change and the formation of new2D stable materials. These 2D materials exhibit relatively unalteredselectivity but diminished CO₂ uptake. This indicates that theSIFSIX-3-M materials series is not sufficiently robust to handle CO₂ andH₂S capture in most critical applications throughout the oil and gas andrenewable fuels industries, especially in applications which bring thematerials into contact with moisture and H₂S.

Provided herein are novel functionalized MOFs suitable for a myriad ofapplications, which exhibit high water vapor and H₂S tolerance andstability over thousands of cycles. For example, efficiency of H₂S andCO₂ separation is enhanced, in part, by the stability of these MOFs inthe presence of water and H₂S. These MOFs eliminate the safety,efficiency, and environmental concerns associated with amine scrubbingtechniques while providing high stability in the presence of water andH₂S. The benefits of this innovative approach include the following: (i)no environmental and safety hazards germane to amine scrubbing (ii) nopreliminary separate desulfurization is necessary (iii) no separate gasdrying is needed, and (iv) no compression-decompression/cooling of NG isrequired. Further, the MOFs provided herein offer exceptional thermaland mechanical stability, particularly during adsorption/desorption.

MOFs, as provided herein, comprise one or more MBBs. Generally, a MBB,or a network of MBBs, can be represented by the formula[(node)_(a)(ligand)_(b)(solvent)_(c)]_(n), wherein n represents thenumber of molecular building blocks. Solvent represents a guest moleculeoccupying pores within the MOF, for example as a result of MOFsynthesis, and can be evacuated after synthesis to provide a MOF withunoccupied pores. Accordingly, the value of c can vary down to zero,without changing the definitional framework of the MOF. Therefore, inmany instances, MOFs as provided herein can be defined as[(node)_(a)(ligand)_(b)]_(n), without reference to a solvent or guestmolecule component.

In some embodiments herein, MOFs can be characterized by the formula[M_(a)M_(b)F_(6-n)(O/H₂O)_(w)(Ligand)_(x)(solvent)_(y)]_(z). In someembodiments, solvent can include a chemical species present afterfabrication of the MOF. In some embodiments, solvent can include afunctionalizing guest molecule, such as water, dimethylformamide (DMF),diethylformamide (DEF), and alcohols, among others. Some embodimentsherein comprise a porous, uninhabited MOF characterized by the formula[(node)_(a)(ligand)_(b)]_(n), wherein node comprises, generally,M_(a)M_(b)F_(x)O_(y)(O/H₂O)_(z). In some embodiments, Ma compriseselements selected from periodic groups IB, IIA, IIB, IIIA, IVA, IVB,VIB, VIIB, or VIII. In some embodiments, Mb comprises elements selectedfrom periodic groups IIIA, IIIB, IVB, VB, VIB, or VIII. In someembodiments, Ma comprises elements selected from periodic groups IB,IIA, IIB, IIIA, IVA, IVB, VIB, VIIB, or VIII and Mb comprises elementsselected from periodic groups IIIA, IIIB, IVB, VB, VIB, or VIII.

In some embodiments, Ma can comprise one of the following cations: Cu2+,Zn2+, Co2+, Ni2+, Mn2+, Zr2+, Fe2+, Ca2+, Ba2+, Pb2+, Pt2+, Pd 2+, Ru2+,Rh2+, Cd2+, Mg+2, Al+3, Fe+2, Fe+3, Cr2+, Cr3+, Ru2+, Ru3+ and Co3. Insome embodiments, Mb can be one of the following Al+3, Fe+2, Fe+3, Cr2+,Cr3+, Ti3+, V3+, V5+, Sc3+, In3+, Nb5+, Y3+. In some embodiments, Ma cancomprise one of the following cations: Cu2+, Zn2+, Co2+, Ni2+, Mn2+,Zr2+, Fe2+, Ca2+, Ba2+, Pb2+, Pt2+, Pd 2+, Ru2+, Rh2+, Cd2+, Mg+2, Al+3,Fe+2, Fe+3, Cr2+, Cr3+, Ru2+, Ru3+ and Co3; Mb can be one of thefollowing Al+3, Fe+2, Fe+3, Cr2+, Cr3+, Ti3+, V3+, V5+, Sc3+, In3+,Nb5+, Y3+. In such embodiments, the ligand can be any bi-functionalN-donor linkers based on monocyclic or polycyclic group (aromatic ornot).

In some embodiments, a ligand can comprise a polydentate, orpoly-functional ligand, such as a bi-functional ligand, a tri-functionalligand, or ligands with four or more functional sites. In someembodiments, a ligand can comprise an N-donor linker. In someembodiments a ligand can comprise a poly-functional ligand. In someembodiments, a ligand can comprise a plurality of N-donor functionalgroups. In some embodiments, a ligand can comprise a monocyclic orpolycyclic group structure, wherein the cyclic groups can be aromatic ornon-aromatic. In some embodiments, a ligand can comprise anitrogen-containing monocyclic or polycyclic group structure. In someembodiments, a ligand can comprise a nitrogen-containing heterocyclicligand, including pyridine, pyrazine, pyrimidine, pyridazine, triazine,thiazole, oxazole, pyrrole, imidazole, pyrazole, triazole, oxadiazole,thiadiazole, quinoline, benzoxazole, benzimidazole, and tautomersthereof.

Some embodiments of suitable MOFs can be represented by the followinggeneral formula:[M_(a)M_(b)F_(6-n)(O/H₂O)_(w)(Ligand)_(x)(solvent)_(y)]_(z) whereinM_(a) can be one of the following cations: Cu2+, Zn2+, Co2+, Ni2+, Mn2+,Zr2+, Fe2+, Ca2+, Ba2+, Pb2+, Pt2+, Pd 2+, Ru2+, Rh2+, Cd2+, Mg+2, Al+3,Fe+2, Fe+3, Cr2+, Cr3+, Ru2+, Ru3+ and Co3; Mb can be one of thefollowing Al+3, Fe+2, Fe+3, Cr2+, Cr3+, Ti3+, V3+, V5+, Sc3+, In3+,Nb5+, Y3+; and the ligand can be any bi-functional N-donor linkers basedon monocyclic or polycyclic group, aromatic or not.

One MOF synthesis strategy provided herein comprises linking inorganicchains using appropriate N-donor based linkers to deliberately generatechannels along one crystallographic direction. The inorganic chains arebuilt up from the trans-connection between M_(a)N₄F₂ and M_(b)F₄(H₂O)₂octahedra or between M_(a)N₄F₂ and M_(b)F₅(H₂O) octahedra or betweenM_(a)N₄F₂ octahedra and M_(b)F₅(O) octahedra. FIG. 1A illustrates anexample of an inorganic chain, built up from M_(a)N₄F₂ and M_(b)F₅(H2O)octahedra. The resulted inorganic chains are linked to each other usingbi-functional N-donor organic ligands, thereby generating channels withdifferent sizes and shapes depending on the nature of the organiclinker. FIG. 1B illustrates a schematic view of one embodiment of a MOFcomprising a NiNbF₅O(pyrazine)₂ structure, viewed along the c-axis.

The novel series of MOFs structures disclosed herein can be designedwith a variety of pore sizes and/or open-metal sites which affordtunable properties for a variety of applications, particularly due to ahigh stability in the presence of water vapor and H2S. Tuning, in someembodiments, can include modification of the organic and/or inorganiccomponents of the MOF. For example, in some embodiments, lightermetal-based clusters can be used to lower the framework density andincrease the relative wt. % of captured CO2 and/or H2S. Further, the MOFplatforms as provided herein allow for an unprecedented high degree oftuning control at the molecular level, allowing the size and shape ofchannels within a MOF architecture to be rigorously controlled andadapted to specific separation of numerous gases, even beyond watervapor and H2S.

The utility of MOFs such as those provided herein are highly dependentupon the framework's structural features such as structural strength,density, functionality, pore aperture dimensions, pore dimensions, theratio of pore aperture dimensions to pore dimensions, poreaccessibility, and the presence of a plurality of pore dimensions and/orpore aperture dimensions (e.g., a poly-porous MOF). Because the MOFsprovided herein are highly tunable, the potential for utility is vast.

The originality of this new class of crystalline porous materials isbased, in part, on the fact that the shape of cavities, (i.e. square orrectangle based channels), is controlled from a structural point of viewusing appropriate cations and organic linkers. The novel MOFarchitectures disclosed herein offer a novel improvement on some MOFarchitectures by replacing silicon components with other metals, such asAl3+, Fe2+, Fe3+, V3+, V4+, V5+, Nb5+, to afford highly stable materialswith or without open metals sites. In some embodiments, the use ofspecific cations, such as Al+3, Fe+2, Fe+3, Cr2+, Cr3+, Ti3+, V3+, V5+,Sc3+, In3+, Y3+, in Mb site positions can introduce open-metal siteswithin the channels that enhance properties of stability, for example.

In some embodiments, a representative[M_(a)M_(b)F_(6-n)(O/H₂O)_(w)(Ligand)_(x)(solvent)_(y)]_(z) MOFstructure can include a Ni M_(a) constituent, an M_(b) constituent groupselected from one of Al, Fe, V, or Nb, and a Ligand comprising apyrazine constituent group. All such embodiments offer high affinity andstability to water vapor and H₂S, unlike the Cu and Zn-based analoguesof SIFSIX-3-M materials made with Si. In in some embodiments a MOFcharacterized by the formula[M_(a)M_(b)F_(6-n)(O/H₂O)_(w)(Ligand)_(x)(solvent)_(y)]_(z) whereinM_(a) equals Ni, M_(b) equals Al, Fe, V or Nb, and ligand equalspyrazine, the pore size (channel size) of the resulting MOF can be about3.3 Å to about 3.8 Å, or about 2.8 Å to about 4.8 Å. In someembodiments, the channels are square/rectangular. In the same or in analternative embodiment, a MOF can have a specific surface area of about250 m2/g to about 500 m2/g. In either of the same MOFs or in analternative embodiment, a MOF can have a pore volume of about 0.1 cm3/gto about 0.25 cm3/g. In a different embodiment, a more elongated ligandcan provide an analogous MOF with much higher porosity.

In some embodiments, M_(b) and/or a ligand can be selected to hinder orallow rotation of a ligand. Altering the nature, shape, and dimensionsof the (M_(b)OF₅)^(x−) pillars employed in[M_(a)M_(b)F_(6-n)(O/H₂O)_(w)(Ligand)_(x)(solvent)_(y)]_(z) MOFs canselectively hinder the free rotation of ligands and thus dictate themaximum and/or minimum opening of the pore aperture size. This approachoffers potential to dial-in/command the passing-blocking of specificprobe molecules. In some embodiments M_(b) and/or a ligand are selectedto allow no rotation of a ligand. In some embodiments M_(b) and/or aligand are selected to allow full rotation of a ligand. In someembodiments M_(b) and/or a ligand are selected to allow partial rotationof a ligand.

In some embodiments, M_(b) and/or a ligand can be selected to hinder orallow rotation of a pillar. Altering the nature, shape, and dimensionsof the (M_(b)OF₅)^(x−) pillars employed in[M_(a)M_(b)F_(6-n)(O/H₂O)_(w)(Ligand)_(x)(solvent)_(y)]_(z) MOFs canselectively hinder the free rotation of pillars and thus dictate themaximum and/or minimum opening of the pore aperture size. This approachoffers potential to dial-in/command the passing-blocking of specificprobe molecules. In some embodiments M_(b) and/or a ligand are selectedto allow no rotation of a pillar. In some embodiments M_(b) and/or aligand are selected to allow full rotation of a pillar. In someembodiments M_(b) and/or a ligand are selected to allow partial rotationof a pillar.

In some embodiments, M_(b) and/or a ligand can be selected to hinder orallow rotation of a ligand and a pillar. Altering the nature, shape, anddimensions of the (M_(b)OF₅)^(x−) pillars employed in[M_(a)M_(b)F_(6-n)(O/H₂O)_(w)(Ligand)_(x)(solvent)_(y)]_(z) MOFs canselectively hinder the free rotation of a ligand and a pillar and thusdictate the maximum and/or minimum opening of the pore aperture size.This approach offers potential to dial-in/command the passing-blockingof specific probe molecules. In some embodiments M_(b) and/or a ligandare selected to allow no rotation of a ligand and a pillar. In someembodiments M_(b) and/or a ligand are selected to allow full rotation ofa ligand and a pillar. In some embodiments M_(b) and/or a ligand areselected to allow partial rotation of a ligand and a pillar.

A specific MOF characterized by the formula [M_(a)M_(b)F_(6-n)(O/H₂O)_(w)(Ligand)_(x)(solvent)_(y)]_(z) is NbOFFIVE-1-Ni, whereinM_(a) comprises Ni and M_(b) comprises Nb. This MOF includes a (NbOF₅)²⁻inorganic pillar which, due to the larger Nb⁺⁵, has a longer Nb—F bondlength (1.905(1) Å) as compared to the Si—F bond length (1.681(1) Å) ofthe SIFSIX MOFs described above. The increased Nb—F bond length reducesthe distance between the pendant fluorine in the channel, and therelatively increased nucleophile behavior of (N_(b)OF₅)²⁻ providesincreased stability in the presence of water. Pyrazine is a suitableligand for the NbOFFIVE-1-Ni MOF, among others as described herein.NbOFFIVE-1-Ni is a pillared sql-MOF based on (NbOF₅)²⁻ pillars thatconnect a 2D square grid of Ni-(pyrazine)₂. The quadrangular-pillaredsql-MOF can be viewed as a 3D MOF wherein each NiOF(pyrazine)₄ nodeserves as 6-connected node connected by (NbOF₅)²⁻ pillars throughfluorine/oxygen atoms giving rise to a pcu topology. It must be notedthat the assignment of one oxygen and one fluorine atom in apicalposition within the pillar has been previously demonstrated in similarmaterials and confirmed with supporting techniques.¹² The overallframework consists of square shaped open channels having slightlysmaller diameters of about 3.175(1) Å (taking account of van der Wallsradii) comparatively to the analogue material SIFSIX-3-Cu (3.980(1) Å).

A specific MOF characterized by the formula [M_(a)M_(b)F_(6-n)(O/H₂O)_(w)(Ligand)_(x)(solvent)_(y)]_(z) is AlFFIVEH₂O-1-Ni, whereinM_(a) comprises Ni and M_(b) comprises Al. When utilizing a pyrazineligand, this MOF can be characterized by the specific formulaNiAlF₅(H₂O)(pyr)₂.2H₂O, although other ligands described herein can besuitable. Another specific MOF characterized by the formula[M_(a)M_(b)F_(6-n)(O/H₂O)_(w)(Ligand)_(x)(solvent)_(y)]_(z) isFeFFIVEH₂O-1-Ni, wherein M_(a) comprises Ni and M_(b) comprises Fe. Whenutilizing a pyrazine ligand, this MOF can be characterized by thespecific formula NiFeF₅(H₂O)(pyr)₂.4H₂O, although other ligandsdescribed herein can be suitable. AlFFIVEH₂O-1-Ni and FeFFIVEH₂O-1-Niare isomorphs, and take advantage of the periodically arrayed fluorinecombined with the adequate one dimensional channel size. In contrast tothe Si of SIFSIX MOFs described above, the introduction of open metalsites within the framework is concomitant with the utilization of anappropriate metal with the required oxidation state that allows thepresence of a water molecule within the metal coordination sphere.Aluminum and Iron cations were used such that the MOF would adopt anoctahedral fluorinated environment and lead to open metal sites aftercoordinated water removal via proper activation. Each isomorph utilizingpyrazine as a ligand exhibits a primitive cubic (pcu) topology resultingfrom the pillaring of metal-pyrazine 2D square-grid moieties with(MF₅H₂O)²⁻ (M=Al³⁺ or Fe³⁺) inorganic pillars. [Consider including FIG.1 from NiAl Natmater 8march to show MOF structure]

Although AlFFIVEH₂O-1-Ni and FeFIVEH₂O-1-Ni are isomorphs to the SiFSIXMOFs described above, the replacement of Si(IV) by Al(III) or Fe(III) isimpossible using similar methods for synethsizing SIFSIX materials whichutilize NiSiF₆ as a cation source. Because no equivalent startingmaterial for Al(III) and Fe(III) exist, new experimental reactionsconditions as described in Examples 2-4 were developed in order tohydrothermally synthesize these two novel fluorinated MOFs in highlyacidic solution.

Some such MOFs can be fabricated using a solvo(hydro)thermal syntheticprocedure. As shown in FIG. 2, a method for fabricating 200 a MOF 230can include combining 205 reactants. Reactants can include one or moreof a fluorhydric acid solution 206 with a Ni2+ source 207, a secondmetal source 208, and a solvent 209 to form a mixture 210. A Ni2+ source207 can include one or more of nickel nitrate, hydrated nickel nitrate,nickel chloride, hydrated nickel chloride, nickel fluoride, hydratednickel fluoride, nickel oxide, or hydrated nickel oxide. The secondmetal source 208 can include an Al+3 source, an Fe+2 source, an Fe+3source, a Cr2+ source, a Cr3+ source, a Ti3+ source, a V3+ source, a V5+source, a Sc3+ source, an In3+ source, a Nb5+ source, a Y3+ source, forexample. These, metals can be in the form of nitrates, hydratednitrates, chlorides, hydrated chlorides, fluorides, hydrated fluorides,oxides, hydrated oxides, and combinations thereof. The solvent 209 caninclude one or more of H₂O, DMF, and DEF. The method for fabricating 200can further comprise allowing the mixture 210 to react 215, sufficientto form a reacted mixture 220. Reacting 215 can include one or more ofcontacting the fluorhydric acid solution 206, the Ni2+ source 207, thesecond metal source 208, and the solvent 209, stirring or agitating themixture 210, or heating the mixture 210. Heating the mixture 210 cancomprise heating to a temperature between about 80° C. to about 200° C.The reacted mixture 220 can be further processed 225 to provide afabricated MOF 230. Processing 220 can include one or more of filteringthe reacted mixture 220, rinsing the reacted mixture 220 with water,removing excess reactants from the reacted mixture 220. In someembodiments, guest molecules are optionally evacuated from a fabricatedMOF 230. Guest molecules can include solvent guest molecules, orderivatives thereof.

In one embodiment, a representative[M_(a)M_(b)F_(6-n)(O/H₂O)_(w)(Ligand)_(x)(solvent)_(y)]_(z) MOFstructure can include a Ni Ma constituent, a Nb Mb constituent group,and a ligand comprising a pyrazine constituent group. FIG. 3Aillustrates powder X-ray diffraction data of this MOF, characterized bythe formula NiNbF₅O(pyrazine)₂(solvent)_(y), confirming the highstability of the MOF in the presence of water. FIG. 3B illustratespowder X-ray diffraction data of this MOF, confirming the high stabilityof the MOF in the presence of H2S.

In some embodiments, one or more MOFs described herein are suitable forapplications involving gas/vapor/solvent dehydration. The particularoutstanding properties of[M_(a)M_(b)F_(6-n)(O/H₂O)_(w)(Ligand)_(x)(solvent)_(y)]_(z) as comparedto SIFSIX-3-M (Cu, Zn, Ni) materials, as well as others known in theart, in terms of stability to moisture, H2O uptake and affinity makethese series of novel MOFs suitable for many industrial applicationwhere various degrees of humidity need to be removed. Furthermore, thesematerials are advantageous in that exposure to moisture in non-processsettings (e.g., transport, installation, maintenance, etc.) will notaffect performance. For example, MOFs, with and without open metalsites, characterized by the formula[M_(a)M_(b)F_(6-n)(O/H₂O)_(w)(Ligand)_(x)(solvent)_(y)]_(z), exhibit anumber advantageous of CO₂ properties (e.g., gas uptake, gasselectivity, kinetics) at various humidity conditions (e.g., up to ca.100% relative humidity.)

These and other results can be expected in similar other embodiments,with or without open metal sites, such as MOF structure characterized bythe formula NiMbF5O(pyrazine)₂, wherein Mb can be one of the followingAl+3, Fe+2, Fe+3, Cr2+, Cr3+, Ti3+, V3+, V5+, Sc3+, In3+, Nb5+, Y3+.These and other results can be expected in similar other embodiments,with or without open metal sites, such as MOF structure characterized bythe formula M_(a)N_(b)F5O(pyrazine)₂, wherein Ma can be one of thefollowing cations: Cu2+, Zn2+, Co2+, Ni2+, Mn2+, Zr2+, Fe2+, Ca2+, Ba2+,Pb2+, Pt2+, Pd 2+, Ru2+, Rh2+, Cd2+, Mg+2, Al+3, Fe+2, Fe+3, Cr2+, Cr3+,Ru2+, Ru3+.

Example 1: Aperture Size Modification

Altering the nature, shape, and dimensions of the pillars employed in[M_(a)M_(b)F_(6-n) (O/H₂O)_(w)(Ligand)_(x)(solvent)_(y)]_(z) MOFs canselectively hinder the free rotation of ligands and thus dictate themaximum and/or minimum opening of the pore aperture size. This approachoffers potential to dial-in/command the passing-blocking of specificprobe molecules. The (NbOF₅)²⁻ pillaring inorganic building block ofNbOFFIVE-1-Ni utilizing a pyrazine ligand demonstrates this approach.Analysis of the NbOFFIVE-1-Ni structure (collected at 100K) revealed theplausible smallest pore window opening associated with the relativelyhindered rotation of the (NbOF₅)²⁻ pillars and the presence of hydrogenbond interactions. As a result, the hydrogen atoms of the pyrazinelinkers circumference the resultant rectangular aperture size of2.838(1) Å, as shown in FIG. 4A, prohibiting the diffusion of anymolecule other than water. In order to gain a better insight on theplausible rotation and tilting of the pyrazine linker and subsequentlyderive a relative maximum opening of the window, providing a gate limitfor the largest molecule to pass through, the same structure wascollected and analysed at room temperature. Noticeably, at roomtemperature, the pyrazine molecules are perceived to freely rotate alongthe N . . . N axis, while the (NbOF₅)²⁻ pillars rotate along the 4-foldaxis, as shown in FIG. 4B. The concurrent pyrazine and pillars (NbOF₅)²⁻mobility afforded a maximum window aperture size of 4.752(1) Å.

Example 2: Synthesis of NbOFFIVE-1-Ni

A NbOFFIVE-1-Ni MOF was synthesized via a solvothermal reactionutilizing a hydrofluoric acid solution of a mixture of Ni(NO₃)₂6H₂O,Nb₂O₅, and pyrazine. The reaction yielded violet, square shaped crystalsof NiNbOF₅(pyrazine)₂.2H₂O which are referred to as NbOFFIVE-1-Ni.Single crystal X-ray diffraction of a single NbOFFIVE-1-Ni crystal at100K revealed that the MOF crystallized in tetragonal space group I4/mcmwith unit cell parameters a=b=9.8884(4) Å and c=15.783(1) Å. Highthermal stability of the material was confirmed by variable-temperaturePXRD performed in the range of 25° C. to 400° C., establishing that thematerial retains its crystallinity over the temperature range. The waterstability of the material was also confirmed via in-situvariable-humidity PXRD up to 95% humidity. Moreover, excellent toleranceto hydrogen sulfide, a feature that is rarely proven for MOFs, wasdemonstrated by PXRD after exposure to H₂S and by collecting adsorptionisotherms of H₂S. Nitrogen adsorption isotherm at 77K performed onactivated material indicated that NbOFFIVE-1-Ni is not porous to N₂.Consequently, adsorption investigation was carried out using smallerprobe molecule than N₂, such as CO₂ (at 273 K) to verify the porousnature of material. The BET specific surface area and pore volume asdetermined from CO₂ adsorption at 273 K is 280 m²/g and 0.095 cm³/g,respectively.

Example 3: Synthesis of AlFFIVEH₂O-1-Ni

An AlFFIVEH₂O-1-Ni MOF characterized by the formulaNiAlF₅(H₂O)(pyr)₂.2H₂O was synthesized by mixing pyrazine (0.3844 g, 4.8mmol, Aldrich), NiNO₃ (0.1745 g, 0.6 mmol, Acros), Al(NO₃)₃ (0.225 g,0.6 mmol) and HF_(aq) 48% (0.255 ml, 6 mmol) and dispersing the mixturein deionized water in a 100 ml Teflon liner. The mixture was placed inan autoclave, and the autoclave was then sealed and heated to 85 C° for24 h. After cooling down, the resulting blue-violet square shapecrystals, suitable for single crystal structure determination, wereseparated by filtration, washed with ethanol and dried in air. N=13.76%(theo. 14.19%), C=21.73% (theo. 24.33%), H=3.16% (theo. 3.57%).AlFFIVEH₂O-1-Ni was activated at 95° C. for one night under high vacuum(3 milliTorrs) before every sorption measurements. All reagents wereused as received from commercial suppliers without further purification.

Single-crystal diffraction experiments revealed that the MOFcrystallized in tetragonal space group I4/mcm. High thermal stability ofthe material was confirmed by variable-temperature PXRD performed up to400° C., establishing that the material retains its crystallinity over abroad temperature range. The water stability of the material was alsoconfirmed via in-situ variable-humidity PXRD up to 95% humidity relativeto calculated theoretical values.

Crystallographic studies revealed the presence of (AlF₅(H₂O))²⁻inorganic building blocks within the framework acting as pillars. Inaddition to water molecules connected to aluminium, thermogravimetricanalysis confirmed the presence of water molecules located within thechannels. The investigation of the electron density within the cavitiesrevealed two crystallographic independent water molecules present withinthe cavities of AlFFIVEH₂O-1-Ni. A hydrogen bond network betweenfluorine atoms of pillars and water guest molecules was revealed, withthe symmetrically generated water molecules connected to each other andto fluorine atoms belonging to the pillars. It must be noted that watermolecules from the pillar are also part of the network.

Example 4: Synthesis of FeFFIVEH₂O-1-Ni

An FeFFIVEH₂O-1-Ni MOF characterized by the formulaNiFeF₅(H₂O)(pyr)₂.4H₂O was synthesized by mixing pyrazine (0.3844 g, 4.8mmol, Aldrich), Ni(NO₃)₂ (0.1745 g, 0.6 mmol, Acros), Fe(NO₃)₃ (0.2323g, 0.6 mmol) and HF_(aq) 48% (0.255 ml, 6 mmol,) and dispersing themixture in deionized water (3 ml) in a 100 ml Teflon liner. The mixturewas placed in an autoclave, and the autoclave was then sealed and heatedto 85 C° for 24 h. After cooling down, the resulting blue square shapecrystals, suitable for single crystal structure determination, wereseparated by filtration, washed with ethanol and dried in air. Noticethat sometimes only light blue powder is obtained. Elemental analysis:N=11.79% (theo. 12.19%), C=20.24% (theo. 20.90%), H=3.53% (theo. 3.95%),0=17.13% (theo. 17.40%). FeFFIVEH₂O-1-Ni was activated at 95° C. for onenight under high vacuum (3 milliTorr) before every sorptionmeasurements. All reagents were used as received from commercialsuppliers without further purification.

Single-crystal diffraction experiments revealed that the MOFcrystallized in tetragonal space group P4/nbm. High thermal stability ofthe material was confirmed by variable-temperature PXRD performed up to250° C., establishing that the material retains its crystallinity over abroad temperature range. The water stability of the material was alsoconfirmed via in-situ variable-humidity PXRD up to 95% humidity relativeto calculated theoretical values.

Crystallographic studies revealed the presence of (FeF₅(H₂O))²⁻inorganic building blocks within the framework acting as pillars. Inaddition to water molecules connected to iron, thermogravimetricanalysis confirmed the presence of water molecules located within thechannels. The investigation of the electron density within the cavitiesrevealed four water molecules present within the cavities ofFeFFIVEH₂O-1-Ni. A hydrogen bond network between fluorine atoms ofpillars and water guest molecules was revealed with the four watermolecules forming a cluster having a tetrahedral shape. It must be notedthat water molecules from the pillar are also part of the network.

What is claimed is:
 1. A metal-organic framework, comprising: a pillarcharacterized by the formula (M_(b)F₅(O/H₂O)), where M_(b) is selectedfrom Al⁺³, Ga³⁺, Fe⁺², Fe⁺³, Cr²⁺, Cr³⁺, Ti³⁺, V³⁺, V⁵⁺, Sc³⁺, In³⁺, andY³⁺; and a square grid characterized by the formula (M_(a)(ligand)_(x)),where M_(a) is selected from periodic groups IB, IIA, IIB, IIIA, IVA,IVB, VIB, VIIB, and VIII, where the ligand is a polyfunctional organicligand, and x is 1 or more; wherein the square grid and pillar associateto form the metal-organic framework.
 2. The metal-organic framework ofclaim 1, wherein M_(a) is selected from Cu²⁺, Zn²⁺, Co²⁺, Ni²⁺, Mn²⁺,Zr²⁺, Fe²⁺, Ca²⁺, Ba²⁺, Pb²⁺, Pt²⁺, Pd²⁺, Ru²⁺, Rh²⁺, Cd²⁺, Mg²⁺, Al⁺³,Fe²⁺, Fe⁺³, Cr²⁺, Cr³⁺, Ru²⁺, Ru³⁺, and Co³⁺.
 3. The metal-organicframework of claim 1, wherein M_(a) is selected from Cu²⁺, Zn²⁺, Co²⁺,Ni²⁺, Mn²⁺, Zr²⁺, Fe²⁺, Ca²⁺, Ba²⁺, Pb²⁺, Pt²⁺, Pd²⁺, Ru²⁺, Rh²⁺, Cd²⁺,Mg²⁺, Fe²⁺, Cr²⁺, and Ru²⁺.
 4. The metal-organic framework of claim 1,wherein M_(a) is selected from Al⁺³, Fe⁺³, Cr³⁺, Ru³⁺, and Co³⁺.
 5. Themetal-organic framework of claim 1, wherein the ligand is a bifunctionalN-donor ligand.
 6. The metal-organic framework of claim 1, wherein theligand includes a monocyclic group structure or a polycyclic groupstructure.
 7. The metal-organic framework of claim 1, wherein the ligandis selected from pyridine, pyrazine, pyrimidine, pyridazine, triazine,thiazole, oxazole, pyrrole, imidazole, pyrazole, triazole, oxadiazole,thiadiazole, quinoline, benzoxazole, and benzimidazole.
 8. Themetal-organic framework of claim 1, wherein the ligand includes one ormore of pyrazine, pyridazine, oxazole, imidazole, pyrazole, andbenzimidazole.
 9. The metal-organic framework of claim 1, wherein theligand includes one or more of thiazole, oxadiazole, thiadiazole, andbenzoxazole.
 10. The metal-organic framework of claim 1, wherein theligand includes one or more of triazine and triazole.
 11. Themetal-organic framework of claim 1, wherein the square grid is(M_(a)(pyrazine)₂).
 12. The metal-organic framework of claim 11, whereinM_(a) is Ni.
 13. The metal-organic framework of claim 11, wherein themetal-organic framework exhibits a primitive cubic (pcu) topology. 14.The metal-organic framework of claim 1, wherein M_(b) is Al⁺³, V³⁺, V⁵⁺,Fe⁺², or Fe⁺³.
 15. The metal-organic framework of claim 1, wherein thepillar is (AlF₅(H₂O))²⁻.
 16. The metal-organic framework of claim 1,wherein the pillar is (FeF₅(H₂O))²⁻.
 17. The metal organic framework ofclaim 1, wherein a pore size of the metal-organic framework ranges fromabout 2.8 Å to about 4.8 Å.
 18. The metal organic framework of claim 1,wherein a pore size of the metal-organic framework ranges from about 3.3Å to about 3.8 Å.
 19. The metal organic framework of claim 1, wherein aspecific surface area of the metal-organic framework ranges from about250 m²/g to about 500 m²/g.
 20. The metal organic framework of claim 1,wherein a pore volume of the metal-organic framework ranges from about0.1 cm³/g to about 0.25 cm³/g.